The Effect Of Organic Inorganic Fertilizer Combination On Carbon Emissions From Paddy Fields And Soil Organic Carbon Storage

The anthropogenic greenhouse gas emissions are the predominant cause of global warming,and the paddy field ecosystem is one of the primary sources of non carbon dioxide greenhouse gas emissions in agricultural production.As clearly revealed in previous studies,long-term and extensive application of fertilizers gives rise to ecological and environmental risks such as soil acid-base imbalance,reduction of organic matter content and deterioration of soil structure.The combined application of organic and inorganic fertilizers such as straw and green manure has significant effects on improving soil fertility,improving soil physical and chemical properties and increasing paddy yield.Nevertheless,the application of organic fertilizers such as straw and green manure heightens the input of soil organic matter,which potentially facilitates methane（CH₄）emissions from paddy fields,triggering an increase in carbon emission intensity of paddy fields.Therefore,optimizing the application method of organic fertilizers and achieving efficient and reasonable combination of organic and inorganic fertilizers is the current research focus on reducing greenhouse gas emissions and increasing sinks in paddy field ecosystem.This study takes paddy fields in Qingpu District,Shanghai as the research object,and sets up six treatments:single application of chemical fertilizer（C1）,application of chemical fertilizer+green manure returning to the field（C2）,application of chemical fertilizer+straw returning to the field（C3）,application of chemical fertilizer+ biogas residue returning to the field（C4）,application of chemical fertilizer+green manure and biogas residue combined returning to the field（C5）and nitrogen reduction by 20%with chemical fertilizer+green manure and biogas residue combined returning to the field（C6）.High frequency continuous monitoring of CH₄ and nitrous oxide（N₂O）emissions from paddy fields using the PICARRO G2508 greenhouse gas online monitoring instrument.In order to grasp the characteristics of carbon emissions from paddy fields under different organic-inorganic fertilizer applications,clarify the impact of different fertilizer applications on carbon emissions from paddy fields,and explore the correlation between CH₄ and N₂O emissions from paddy fields and temperature,water and soil factors.On this basis,based on field monitoring data,verify the feasibility of applying the DNDC model to paddy fields in Shanghai,and further simulate the dynamic changes of soil organic carbon（SOC）pool in paddy fields under different organic-inorganic fertilizer applications in the next 50 years.Combined with the net global warming potential（NGWP）,clarify the comprehensive impact of different fertilizer applications on soil SOC accumulation and greenhouse gas emissions from paddy fields.The main conclusions are as follows:（1）CH₄ and N₂O emissions are mainly concentrated in the paddy season.Compared with the fallow season,the cumulative emission of CH₄ in the paddy season accounts for more than 99%of the total annual emissions,while the cumulative N₂O emissions accounted for 87.76%to 97.87%of the total annual emissions.During the paddy season,the CH₄ emission mainly occur in the tillering stage and booting stage,respectively accounting for 58.45%～83.76%and 10.53%～29.07%of the cumulative CH₄ emissions,while the N₂O emission mainly occur in the tillering and maturity stages,respectively accounting for 32.25%～45.08%and 53.3 8%～64.64%of the cumulative N₂O emissions.The roasting treatment increased CH₄ emissions and decreased N₂O emissions.During this period,the CH₄ emission flux of each treatment decreased from 45.30～314.22 mg CH₄·m-2·d-1 to 2.43-44.52 mg CH₄·m-2·d-1,and the N₂O emission flux increased from 1.29～3.84 mg N₂O·m-2·d-1 to 13.66～52.06 mg N₂O·m-2·d-1.The cumulative emission of CH₄ in the rice season under different fertilizer applications was 18.77～119.87 kg CH₄·hm-2·a-1,and the cumulative emission of N₂O was 1.20～5.12 kg N₂O·hm2·a-1;Compared with the-single application of chemical fertilizers（C1）.combined application of organic-inorganic fertilizers increased CH₄ emissions by 169.47%～538.63%,and reduced N₂O emissions by 10.35%～76.56%;In the combined application of organic-inorganic fertilizers（C2 to C6）,the global warming potential（GWP）caused by CH₄ emissions accounts for 66.18%～82.48%of the overall GWP of paddy fields,and the reduction of greenhouse gas emissions in paddy fields should focus on reducing CH₄ emissions;Compared with single application of chemical fertilizers（C1）,application of chemical fertilizers+biogas residue returning（C4）increased rice yield by 11.88%,while reducing GWP and greenhouse gas emission intensity（GHGI）by 7.87%and 21.05%,respectively.（2）The CH₄ emission flux from paddy fields shows a extremely significant positive correlation with air temperature,soil temperature at a depth of 5 cm,soil SOC content,soil soluble organic carbon（DOC）content and soil ammonium nitrogen（NH4+-N）content.It also shows a significant or extremely significant negative correlation with the dissolved oxygen（DO）content in surface water and soil pH.Among them,soil pH,soil SOC content,soil DOC content and soil N H4+-N content has a significant impact on CH₄ emissions.They are the key influencing factors for CH₄ emissions from paddy fields.N₂O emission flux from paddy fields shows a significant or extremely significant positive correlation with air temperature,soil temperature at a depth of 5 cm,DO content in surface water,NH4+-N concentration in surface water,nitrate nitrogen（NO3--N）concentration in surface water and soil soluble organic nitrogen（DON）content.Among them,air temperature,soil temperature at a depth of 5 cm and NH4+-N concentration in surface water has a significant impact on N₂O emissions.They are the key influencing factors for N₂O emissions from paddy fields.（3）The DNDC model has good simulation effects on paddy yield,soil SOC content and CH₄ and N₂O emissions from paddy fields under different fertilizer applications in Shanghai.Although the model did not capture certain greenhouse gas emissions peak well,most of the simulated and observed values have a high degree of agreement,with root mean square error（RMSE）ranging from 12.72%to 24.12%;On a time scale of 50-year scale,the combined application of organic-inorganic fertilizers（C2 to C6）increased the soil SOC content by 46.48%～68.65%compared with the initial value.Soil SOC accumulation,among them,the application of chemical fertilizer+straw returning（C3）and the application of chemical fertilizer+biogas residue returning（C4）have better SOC accumulation effects,and the average annual accumulation of soil SOC in the two is 0.24 g kg-1·a-1 and 0.17 g·kg-1·a-1;Considering the effects of different fertilizer applications on soil SOC storage and rice field greenhouse gas emissions,among the fertilizer application methods investigated in this study,the NGWP of chemical fertilizer+biogas residue returning（C4）was the lowest,which was 1542.05 kg CO2eq hm-2·a-1,the straw is made into biogas residue through anaerobic fermentation and then returned to the field,which not only provides low-carbon biomass energy for the soil,but also realizes the reduction of greenhouse gas emissions in the paddy field.It is a straw with both environmental and economic benefits treatment and application of organic fertilizers.